1. Field of the Invention
The present invention relates generally to controlling the growth of microorganisms. More specifically, the present invention relates to the use of compositions for inhibiting the growth of microorganisms in industrial waters.
2. Description of the Prior Art
The presence of microorganisms in waters, especially industrial waters, is a never-ending concern for industrial manufacturers. Examples of industrial waters where microorganisms can interfere with industrial processes include: cooling tower waters; mining process waters; food processing waters; sugar reprocessing waters; and the like.
In the paper industry, the growth of microorganisms in pulp and paper mill waters can adversely affect finished paper products. Microbial life depends on the nutrient supply, the pH and the temperature of a particular system. The warm temperatures and rich carbohydrate containing fluids of paper machines and process streams provide ideal growth conditions for a variety of microorganism. These contaminating microorganisms are capable of causing spoilage of pulp, furnish, or chemical additives. The microorganisms cause deposits that break loose and fall into the paper furnish, resulting in quality loss and/or end product defects such as holes and spots. The end result is unsalable paper or paper sold at a lower value.
The presence of microorganisms within industrial water systems results in the formation of deposits of biological origin on industrial machines. These formation deposits give rise to corrosion, breaks, increased down time, loss of yield, high chemical costs, odors and expensive deposit control programs. In the paper mill industry, slime deposit is reportedly responsible for nearly 70% of all breaks, blockages and pump failures.
Slime may be defined as an accretion or accumulation caused by certain micro-organisms in the presence of pulp fiber, filler, dirt and other materials, mixed in varied proportions, having variable physical characteristics and accumulating at continuous changing rates. In most industrial process waters, especially pulp and paper mill systems, spore forming bacteria and Pseudomonas aeruginosa contribute to slime formation. The later is most prevalent in paper mill slimes. Fungi is also a contributor toward slime formation.
The conventional method of controlling microbial growth is through the use of biocides. Biocides are generally divided into two main groups: oxidizing and non-oxidizing. These biocides act on the microorganisms by attacking them in one of three ways: by attacking the cell wall; the cytoplasmic membrane; or the cellular constituents.
One method is embodied in U.S. Pat. No. 4,802,994 issued Feb. 7, 1989 to Mouche, et al. The Mouche reference teaches the use of a composition containing hydrogen peroxide and glutaraldehyde to industrial process water to control the growth of microorganisms. However, the Mouche reference is specifically designed to counteract the growth of anaerobic organisms. Such a use of oxidants to counteract anaerobic organisms is appropriate since oxidants are toxic to anaerobic organisms as a result of the oxygen contained within them. Oxygen is, by nature, toxic to anaerobes. Aerobic organisms, in contrast, require oxygen in order to survive. As a result, no attempt has been made to use oxidants as an effective method of controlling the growth of aerobic microorganisms.
While biocides do inhibit microbial growth, economic and environmental concerns require improved methods. A problem with the use of biocides is that high levels of expensive chemicals are needed to control microbial growth. To date, none of the commercially available biocides have exhibited a prolonged biocidal effect. Their effectiveness is rapidly reduced as a result of exposure to physical stresses such as temperature or association with ingredients contained by the system toward which they exhibit an affinity. This results in a reduction or elimination of their biocidal effectiveness. Therefore, the use of such biocides involves continuous or frequent additions to paper mill systems. Further, these additions must be made at a plurality of points or zones in the system. The costs of the biocides and the labor costs involved are considerable.
Moreover, such chemicals are highly toxic in the quantities known to be required for effective control of microbial populations. As a result, environmental regulations restrict the amount of biocides that can safely be discarded into the environment. Therefore, a need exists for improved methods for controlling the growth of microorganisms in industrial process waters.